Porphyrin photodynamic therapy (PDT) is a new form of cancer therapy. Cancer treatment with porphyrin-PDT uses the combination of a photosensitizing drug (a porphyrin) and a high intensity light source. Hematoporphyrin derivative (HpD) is currently the most widely used porphyrin for PDT. After systemic administration, HpD is selectively retained in neoplastic tissue. When a porphyrin-laden neoplasm is illuminated with visible light, a photodynamic reaction is initiated which results in tumor destruction. The most versatile and efficient light source for this therapy is a laser system--an argon/dye laser system. funds are requested for the purchase of the Aurora/M argon/dye laser system (Cooper Laser Sonics, Inc.) for expanding the research into porphyrin photodynamic therapy for cancer. This instrument would be used to: 1. Continue and expand the study of the effect of porphyrin-PDT on blood flow to tumors and normal tissue in rats and dogs. 2. Study the combined use of porphyrin-PDT and hyperthermia in the treatment of spontaneous dog tumors. 3. Explore the potential of porphyrin-PDT in the treatment of experimentally induced esophageal tumors. 4. Test in vitro and in vivo new tetrapyrolle compounds recently synthesized as photosensitizing agents for PDT. Based upon the experience gained in animal studies, our long term objective is to develop protocols for pilot research studies in humans using porphyrin-PDT.